Transcript Dev. Male Gen. Sys

MALE GENITAL
SYSTEM
Dr. Mujahid Khan
Development of Gonads
The gonads are derived from 3 sources:
 The
mesothelium (mesodermal epithelium)
lining the posterior abdominal wall
 The
underlying mesenchyme (embryonic
connective tissue)
 The
primordial germ cells
Indifferent Gonads
 The
initial stages of gonadal development
occur during the fifth week
A
thickened area of mesothelium develops
on the medial side of the mesonephros
 Proliferation
of this epithelium and the
underlying mesenchyme produces a bulge
on the medial side of the mesonephros
called Gonadal ridge
Indifferent Gonads

Finger like epithelial cords or Gonadal cords
soon grow into the underlying mesenchyme

The indifferent gonad now consists of an
external cortex and an internal medulla

In embryos with an XX sex chromosome
complex, the cortex differentiates into an ovary
and the medulla regresses

In embryos with an XY sex chromosome
complex, the medulla differentiates into a testis
and the cortex regresses
Primordial Germ Cells

These large, spherical cells are visible early in the fourth
week among the endodermal cells of the yolk sac near
the allantois

During folding of the embryo, the dorsal part of the yolk
sac is incorporated into the embryo

With this the primordial germ cells migrate along the
dorsal mesentery of the hindgut to the gonadal ridges

During the sixth week the primordial germ cells enter the
underlying mesenchyme and are incorporated in the
gonadal cords
Sex Determination
 Chromosomal
and genetic sex is
determined at fertilization
 It
depends upon whether an X-bearing
sperm or a Y-bearing sperm fertilizes the
X-bearing ovum
 The
type of gonads develop is determined
by the sex chromosome complex of the
embryo (XX or XY)
Sex Determination

Before the seventh week, the gonads of the two
sexes are identical in appearance called
indifferent gonads

Development of the male phenotype requires a
Y chromosome

The SRY gene for a testes-determining factor
(TDF) has been localized in the sex-determining
region of the Y chromosome

Two X chromosomes are required for the
development of the female phenotype
Sex Determination

The Y chromosome has a testes-determining effect on
the medulla of the indifferent gonad

The absence of a Y chromosome results in the formation
of an ovary

Testosterone, produced by the fetal testes, determines
the maleness

Primary female sexual differentiation in the fetus does
not depend on hormones

It occurs even if the ovaries are absent
Development of Testes

Embryos with a Y chromosome usually develop
testes

The SRY gene for TDF on the short arm of the Y
chromosome acts as the switch that directs
development of indifferent gonad into testes

TDF induces the gonadal cords to condense and
extend into the medulla of indifferent gonad,
where they form rete testes
Development of Testes
 The
connection of gonadal cords or
seminiferous cords with the surface
epithelium is lost as tunica albuginea
develops
 The
development of a dense tunica
albuginea is the characteristic feature of
testicular development in a fetus
Development of Testes

The enlarging testis separates from the
degenerating mesonephros and becomes
suspended by its own mesentery called
mesorchium

The seminiferous cords develop into the
seminiferous tubules, tubuli recti, and rete testis

The seminiferous tubules are separated by
mesenchyme that gives rise to the interstitial cell
of Leydig
Development of Testes

By the eighth week, these cells begin to secrete
testosterone and androstenedione

These hormones induce masculine
differentiation of the mesonephric ducts and
external genitalia

Testosterone production is stimulated by HCG

Fetal testes also produces a glycoprotein called
antimullerian hormone (AMH) or mullerian
inhibiting substance (MIS)
Development of Testes
 AMH
is produced by sustentacular cells of
Sertoli
 AMH
suppresses development of the
paramesonephric ducts
 Seminiferous
puberty
tubules remain solid until
Development of Testes
 The
walls of seminiferous tubules are
composed of two kinds of cells
 Sertoli
cells, supporting cells derived from
the surface epithelium on the testis
 Spermatogonia,
primordial sperm cells
derived from the primordial germ cells
Development of Testes
 The
rete testis becomes continuous with
15 to 20 mesonephric tubules that become
efferent ductules
 These
ductules are connected with the
mesonephric duct
 It
becomes the duct of the epididymis
Development of Genital Ducts

Both male and female embryos have two pairs of genital
ducts

The mesonephric ducts (wolffian ducts) play an
important role in the development of the male
reproductive system

The paramesonephric ducts (mullerian ducts) have a
leading role in the development of the female
reproductive system

Till the end of sixth week, the genital system is in an
indifferent state, when both pairs of genital ducts are
present
Development of Male Genital Ducts

Distal to the epididymis, the mesonephric duct
acquires a thick investment of smooth muscle
and becomes the ductus deferens

A lateral outgrowth from the caudal end of each
mesonephric duct gives rise to the seminal
gland or vesicle

The secretion from this pair of glands nourishes
sperms

The mesonephric duct between the duct of this
gland and the urethra becomes the ejaculatory
duct
Prostate

Multiple endodermal outgrowths arise from the
prostatic part of the urethra

Grow into surrounding mesenchyme

The glandular epithelium of the prostate
differentiates from these endodermal cells

The associated mesenchyme differentiates into
the dense stroma and smooth muscle of the
prostate
Development of External Genitalia
 Up
to the seventh week of development
the external genitalia are similar in both
sexes
 Distinguishing
sexual characteristics begin
to appear during the ninth week
 External
genitalia are not fully
differentiated until the twelfth week
Development of External Genitalia

Early in the fourth week, proliferating
mesenchyme produces a genital tubercle in both
sexes at the cranial end of the cloacal
membrane

Labioscrotal swelling and urogenital folds soon
develop on each side of the cloacal membrane

The genital tubercle soon elongates to form a
primordial phallus
Development of External Genitalia
 When
the urorectal septum fuses with the
cloacal membrane, it divides it into a
dorsal anal membrane and a ventral
urogenital membrane
 The
urogenital membrane lies in the floor
of a median cleft, the urogenital groove,
which is bounded by urogenital folds
Development of Male External
Genitalia
 Masculization
of the indifferent external
genitalia is induced by testosterone
 The
phallus enlarges and elongates to
become the penis
 The
urogenital folds form the lateral walls
of the urethral groove on the ventral
surface of the penis to form the spongy
urethra
Development of Male External
Genitalia

The surface ectoderm fuses in the median plane
of the penis, forming a penile raphe and
enclosing the spongy urethra within the penis

At the tip of the glans of the penis, an
ectodermal ingrowth forms a cellular ectodermal
cord

It grows towards the root of the penis to meet
the spongy urethra
Development of Male External
Genitalia
 This
cord canalizes and joins the
previously formed spongy urethra
 This
completes the terminal part of the
urethra and moves the external urethral
orifice to the tip of the glans of the penis
 During
the twelfth week, a circular
ingrowth of ectoderm occurs at the
periphery of the glans penis
Development of Male External
Genitalia
 When
this ingrowth breaks down, it forms
the prepuce (foreskin)
 It
is adherent to the glans for some time
 Usually
not easy to retract at birth
 Corpora
cavernosa and corpus
spongiosum of the penis develop from
mesenchyme in the phallus
Development of Male External
Genitalia
 The
labioscrotal swellings grow towards
each other and fuse to form the scrotum
 The
line of fusion of these folds is clearly
visible as the scrotal raphe
 Agenesis
anomally
of scrotum is an extremely rare
Development of Inguinal Canals
 Inguinal
canals develop in both the sexes
 The
gubernaculum passes obliquely
through the developing anterior abdominal
wall at the site of future inguinal canal
 The
gubernaculum attaches caudally to
the internal surface of the labioscrotal
swellings
Development of Inguinal Canals
 The
processus vaginalis develops ventral
to the gubernaculum and herniates
through the abdominal wall along the path
formed by the gubernaculum
 The
vaginal process carries extensions of
the layers of the abdominal wall before it,
which form the walls of the inguinal canal
Development of Inguinal Canals
 In
males, these layers also form the
coverings of the spermatic cord and testis
 The
opening in the transversalis fascia
produced by the vaginal process becomes
the deep inguinal ring
 The
opening created in the external
oblique aponeurosis forms the superficial
inguinal ring
Descent of Testes
Testicular descent is associated with:

Enlargement of the testes and atrophy of the
mesonephroi, allow caudal movement of the
testes

Atrophy of paramesonephric ducts enables
testes to move transabdominally to the deep
inguinal rings

Enlargement of processus vaginalis guides the
testes through the inguinal canal into the
scrotum
Descent of Testes

By 26 weeks the testes have descended
retroperitoneally to the deep inguinal rings

This change in position occurs as the fetal pelvis
enlarges and the trunk of the embryo elongates

Little is known about cause of testicular descent

The process is controlled by androgens
Descent of Testes

Passage of testis through the inguinal canal may
also be aided by the increase in intra-abdominal
pressure resulting from growth of abdominal
viscera

Descent of testes through the inguinal canals
into the scrotum usually begins during 26th week

It takes 2 to 3 days
Descent of Testes

More than 97% of full-term newborn males have
both testes in the scrotum

During the first 3 months after birth, most
undescended testes descend into the scrotum

Spontaneous testicular descent does not occur
after the age of one year

When the testis descends, it carries its ductus
deferens and vessels with it
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